In accordance with U.S. Pat. No. 3,911,041, methanol or dimethyl ether is subjected to the action, at a temperature of at least about 300° C., with a catalyst comprising a crystalline aluminosilicate zeolite having a silica to alumina ratio of at least about 12, a constraint index of about 1 to 12, and containing phosphorus incorporated with the crystal structure thereof in an amount of at least about 0.78 percent by weight. The amount of the phosphorus incorporated with the crystal structure of the zeolite may be as high as about 4.5 percent by weight. The zeolite, preferably, also has a dried crystal density of not less than about 1.6 grams per cubic centimeter. The crystalline aluminosilicate zeolite having a silica to alumina ratio of at least about 12 is first converted to the hydrogen form, then phosphorus is introduced by reaction with a phosphorus-containing compound having a covalent or ionic constituent capable of reacting or exchanging with hydrogen ion and thereafter heating. There is no steaming of the zeolite prior to introduction of phosphorus. Preferably, prior to reacting the zeolite with the phosphorus-containing compound, the zeolite is dried. Drying can be effected in the presence of air. Elevated temperatures may be employed.
In accordance with U.S. Pat. No. 5,573,990 methanol and/or dimethylether is converted in presence of a catalyst which contains at least 0.7% by weight of phosphorus and at least 0.97% by weight of rare earth elements incorporated within the structure of the catalyst. Preferably the amount of phosphorus is comprised between 0.7 and 5% by weight. The phosphorus content in the catalyst is most preferably comprised between 1.3 and 1.7% by weight. The rare earth elements incorporated with the crystal structure of the catalyst are preferably rich in lanthanum, the content of lanthanum in the catalyst being preferably comprised between 2.5 and 3.5% by weight. The zeolite ZSM-5 based catalyst presents a mole ratio SiO2/Al2O3 comprised between 40 and 80, a crystal size comprised between 1 and 10 μm and adsorption capacities of n-hexane and water 10-11% by weight and 6-7% by weight respectively. Said ZSM-5 is synthesized in the presence of a template, then is converted to the hydrogen form by ion exchange with hydrochloric acid. The zeolite HZSM-5 prepared as described above is impregnated in aqueous phosphoric acid solution under reduced pressure preferably comprised between 0.08 and 0.09 MPa for 2-3 hours. It is dried at <110° C. for 3-5 hours and calcined at about 540° C. for about 3 hours, the phosphorus content of the obtained product PZSM-5 being 0.7-5% (by weight). There is no steaming of the zeolite prior to introduction of phosphorus. The feedstock methanol comprises steam in a ratio methanol/steam 10-50/90-50, the examples are made with a ratio 30/70.
U.S. Pat. No. 6,797,851 uses at least two different zeolite catalysts to produce an olefin composition from an oxygenate, for example, two different ZSM-type catalysts, to produce olefin having a significant quantity of ethylene and propylene. The catalysts can be mixed together in one reactor, arranged in separate beds, or used in separate reactors in series. It is desirable that one of the zeolite catalysts contains a ZSM-5 molecular sieve. The ZSM-5 molecular sieve is selected from the group consisting of an unmodified ZSM-5, a phosphorous modified ZSM-5, a steam modified ZSM-5 having a micropore volume reduced to not less than 50% of that of the unsteamed ZSM-5, and mixtures thereof. It is also desirable to have a second zeolite catalyst which contains a zeolite molecular sieve selected from the group consisting of 10-ring zeolites such as ZSM-22, ZSM-23, ZSM-35, ZSM-48, and a mixture thereof. In one embodiment, the zeolite employed in the first stage of the above process is ZSM-5 having a silica to alumina molar ratio of at least 250, as measured prior to any treatment of the zeolite to adjust its diffusivity. According to one embodiment, the zeolite is modified with a phosphorous containing compound to control reduction in pore volume. Alternatively, the zeolite is steamed, and the phosphorous compound is added prior to or after steaming. After contacting with the phosphorus-containing compound, the porous crystalline material, according to one embodiment, is dried and calcined to convert the phosphorus to an oxide form. One or more inert diluents may be present in the oxygenate feedstock. Preferred diluents are water and nitrogen. Water can be injected in either liquid or vapor form. For example, the process may be conducted in the presence of water such that the molar ratio water to methanol in the feed is from about 0.01:1 to about 10:1.
US 20060106270A1 relates to a process wherein the average propylene cycle selectivity of an oxygenate to propylene (OTP) process using a dual-function oxygenate conversion catalyst is substantially enhanced by the use of a combination of: 1) moving bed reactor technology in the hydrocarbon synthesis portion of the OTP flow scheme in lieu of the fixed bed technology of the prior art; 2) a hydrothermally stabilized and dual-functional catalyst system comprising a molecular sieve having dual-function capability dispersed in a phosphorus-modified alumina matrix containing labile phosphorus and/or aluminum anions; and 3) a catalyst on-stream cycle time of 400 hours or less. The use of a mixture of a zeolitic catalyst system with a non-zeolitic catalyst system is described. This mixed catalyst embodiment can be accomplished either using a physical mixture of particles containing the zeolitic material with particles containing the non-zeolitic material or the catalyst can be formulated by mixing the two types of material into the phosphorus modified aluminum matrix in order to form particles having both ingredients present therein. In either case the preferred combination is a mixture of ZSM-5 or ZSM-11 with SAPO-34 in relative amounts such that ZSM-5 or ZSM-11 comprises 30 to 95 wt % of the molecular sieve portion of the mixture with a value of about 50 to 90 wt % being especially preferred. It doesn't describe phosphorus modified molecular sieves. A diluent is preferably used in order to control partial pressure of the oxygenate reactant in the OTP conversion zone and in order to shift the overall reaction selectivity towards propylene. An especially preferred diluent for use is steam since it is relatively easily recovered from the product effluent stream utilizing condensation techniques. The amount of diluent used will be selected from the range from about 0.1:1 to 5:1 moles of diluent per mole of oxygenate and preferably 0.5:1 to 2:1 in order to lower the partial pressure of the oxygenates to a level which favours production of propylene.
EP448000 relates to a process for the conversion of methanol or dimethylether into light olefins in presence of water vapour over a silicoaluminate of the pentasil structure of at least Si/Al ratio of 10, producing at least 5 wt % of ethylene, at least 35 wt % of propylene and at most 30 wt % butenes by (1) using a total pressure of 10 to 90 kPa, (2) a weight ratio of water to methanol of 0.1 to 1.5, (3) a reactor temperature of 280 to 570° C. and (4) a proton-containing catalyst of the pentasil-type, having an alkali-content of at most 380 ppm, less than 0.1 wt % of ZnO and less than 0.1 wt % of CdO and a BET surface area of 300 to 600 m2/gram and a pore volume of 0.3 to 0.8 cm3/gram.
The phosphorus modified molecular sieves of the present invention is prepared based on zeolite with low Si/Al ratio (advantageously below 30) preferably synthesized without direct addition of organic template, then the zeolite is subjected to a steam treatment at high temperature before a leaching step with acid solution containing the source of phosphorus which removes advantageously at least 10% of the Al from the zeolite and which leads to at least 0.3 wt % of P on the zeolite. It has been found that phosphorus acid are very efficient in complexing the extra-framework aluminiumoxides and hence removing them from the zeolite solid material. Unexpectedly, a larger quantity of phosphorus than what could be expected from the typical pore volume of the zeolite and assuming that the pores of the zeolites are filled with the used phosphorus acid solution, stays in the solid zeolite material. The chemical functionalities of aluminum with phosphorus in the P-zeolite inhibit the further dealumination of zeolites, which, in turn, increases their stability and selectivity.
The zeolite can be MFI, MOR, MEL, clinoptilolite or FER crystalline aluminosilicate molecular sieves having a low initial Si/Al ratio (advantageously below 30) and preferably synthesized without direct addition of organic directing agent.
The method consists in steaming followed by leaching by a solution of phosphoric acid or by any acid solution containing the source of P. It is generally known by the persons in the art that steam treatment of zeolites, results in aluminium that leaves the zeolite framework and resides as aluminiumoxides in and outside the pores of the zeolite. This transformation is known as dealumination of zeolites and this term will be used throughout the text. The treatment of the steamed zeolite with an acid solution results in dissolution of the extra-framework aluminiumoxides. This transformation is known as leaching and this term will be used throughout the text. Then the zeolite is separated, advantageously by filtration, and optionally washed. A drying step can be envisaged between filtering and washing steps. The solution after the washing can be either separated, by way of example, by filtering from the solid or evaporated.
The residual P-content is adjusted by P-concentration in the leaching solution, drying conditions, and washing procedure if any. This procedure leads to dealumination of zeolites and retention of P. Advantageously, at least 0.3 wt % of P is retained after dealumination on zeolite. Both factors dealumination and the retention of P stabilize the lattice aluminium in the zeolitic lattice, thus avoiding further dealumination. This leads to higher hydrothermal stability, tuning of molecular sieves properties and adjustment of acid properties. The degree of dealumination can be adjusted by the steaming and leaching conditions.
The P-modified zeolites of this recipe are obtained based on cheap crystalline alumosilicates with low Si/Al ratio preferably synthesized without direct addition of organic template. This provides a lower final catalyst cost and makes a preparation procedure more environmentally friendly. The recipe simplifies the procedure for P-ZSM preparation and allows adjusting the Si/Al ratio and P-content in the catalyst. The catalysts show high C3− yield, high C3−/C2− ratio, high stability, high C3's purity and reduced selectivity to paraffin's and to aromatic in XTO. These catalysts provide also the additional flexibility for ethylene and C4+ recycling for additional propylene production. The average propylene yield can be substantially enhanced by using these catalysts in a combination of XTO and OCP process.